In the later RWDs, heated mirror failures are often oxidized connectors on the back side of the mirror. If you can tip the mirror far enough and get a light to see the wires then try using bent needle nose pliers to loosen (not remove), wiggle and reseat the connector. Best access is usually with the mirror pushed all the way around, the glass tipped out as far as it will go, pressing down on one of the far corners to see behind the glass with a good LED flashlight. If that fixes it then you will want to pop the mirror and properly cleanup the contacts. Mirror removal procedures vary by year and model, so look up how your particular glass is mounted in the housing and how to remove it otherwise you risk breaking something. An interim fix is to try getting some spray DeoxIT on the contacts. I think it was Randy Starkie here who got me onto that fix.

Still crossing my fingers for you on that SRS light staying out. It was a good learning exercise and I'm glad my previous experience and finding reference materials were able to help you.